In one aspect, this invention relates to the treatment of spent refinery or petrochemical plant caustic. In another aspect, this invention relates to a process for sulfur removal and recovery from refinery and petrochemical plant streams. In yet another aspect, this invention pertains to apparatus for carrying out the treatment of refinery and petrochemical plant streams.
Petroleum refineries and petrochemical plants use catalytic cracking and thermal cracking processes such as fluid or delayed coking to convert heavy hydrocarbons into lighter cuts. Cuts ranging in boiling point from fuel gas to kerosene are produced. These are often treated with aqueous solutions of sodium hydroxide or potassium hydroxide to remove acidic components such as hydrogen sulfide, mercaptans and phenols. Other refinery operations such as crude oil distillation produce cuts that are often treated in a similar way. The caustic scrubbing liquor retains these compounds as sodium or potassium salts such as sodium sulfide, sodium mercaptide, etc. A purge stream of spent caustic scrubbing liquor is discharged. This spent caustic scrubbing liquor is classified as D003 (Reactive Sulfide) Resource Conservation and Recovery Act (RCRA) hazardous waste. As such, these spent caustic liquors must be treated to a standard of "deactivation to remove the characteristic of reactivity."
A process for deactivating the spent caustic for proper and safe disposal would be very desirable.